In recent years, ceramics has electric properties such as insulating or dielectric properties so that it is used as a material for electronic parts such as ceramic packages. These electronic parts are configured by housing semiconductor elements (e.g., diodes as light emitting elements, thyristors or transistors) in the ceramic package and by arranging circuits or the like to be connected with the semiconductor elements in the package body. When such circuits are to be arranged, a metallic layer for functioning as a circuit pattern may have to be formed on the surface of the package body by using a conductor such as copper or silver. In order to reflect the light efficiently from the light emitting element, the metallic layer for functioning as the optical reflector may also have to be formed of a conductor (e.g., silver) having excellent reflecting properties on the surface of the package body around the light emitting element.
In case the metallic layer is formed on the surface of the package body, the metallic layer and the ceramics have different coefficients of thermal expansion. When the package is subjected to a temperature change, a strain may occur in the vicinity of the boundary between the ceramics and the metallic layer. In case, moreover, the metallic layer is composed of a plurality of layers of metallic materials of different coefficients of thermal expansion, strains may occur in the vicinity of the boundaries of the individual layers may occur due to the temperature change. In order to avoid this situation, there has been proposed a ceramic package (as referred to JP-A-2004-207258 and JP-A-2004-207672), in which the individual layers (i.e., a metallized layer, a nickel-plated layer and a silver-plated layer) have been prevented in the prior art from being peeling off due to the thermal stress, by forming the metallized layer containing tungsten and molybdenum in ceramics and by adhering a nickel-plated layer and a silver-plated layer (having a thickness of 0.1 to 3 μm) to that metallized layer.